1. Field of the Invention
This invention relates to the field of spread spectrum wireless communications or any field that uses Pseudorandom Noise (PN) sequences. For communications applications, PN sequences are generally cyclically repeating sequences of digital 1's and 0's which exhibit certain pseudorandom properties, and are typically generated using a Linear Feedback Shift Register (LFSR).
2. Description of the Related Art
Some applications allow for "sleep" periods, during which the PN sequence may not be needed. An example is a Direct Sequence Spread Spectrum (DSSS) cellular system using long duration, rapidly switching (between pseudorandom 1's and 0's) PN sequences. Cellular systems generally include provision for a sleep mode during which it is not necessary for the Mobile Station (MS), such as a hand held cellular phone, to receive the transmission from the Base Station (BS). In this way portions of the mobile unit can be powered down during the sleep period and the average power drain can be decreased, thereby increasing the standby time of the battery powered unit.
At the end of a sleep period in a DSSS system, it is necessary for the MS to have a local version of the PN sequence which is synchronized to that of the BS. Prior art designs maintain a high speed clock for the purpose of maintaining the synchronization of the PN sequence during sleep. There is no capability of turning off this high speed clock and maintaining PN sequence synchronization. Since the prior art requires the maintenance of a high speed clock, the average power drain of the unit is higher than it would be if this clock source could be turned off.
Therefore, an object of this invention is to optimally use this sleep period by turning off as many electronic components in the system as possible, particularly when a long duration rapidly switching PN sequence must be maintained.